Refrigerating Circuit And Method Of Selectively Cooling Or Defrosting An Evaporator Thereof

ABSTRACT

A Refrigerating circuit according to the invention comprises a compressor, a condenser/gas cooler, an expansion device ( 2 ), an evaporator ( 4 ), and refrigerant conduits circulating a refrigerant therethrough. The evaporator ( 4 ) comprises refrigerant piping comprising a plurality of substantially horizontal layers ( 8, 10 ) each layer comprising a plurality of pipes ( 8   a - 8   h ,  10   a - 10   h ) the pipes being substantially perpendicular to an air flow direction ( 12 ) from an air inlet region to an air outlet region of the evaporator ( 4 ). A pipe selected from the group of the second pipe ( 8   b ) to the last but one pipe ( 8   g ) in the bottom layer ( 8 ) forms the entry pipe ( 8   c ) of the evaporator ( 4 ). The entry pipe ( 8   c ) is connectable with the expansion device ( 2 ) to provide a refrigerating mode, and the entry pipe ( 8   c ) is connectable with a hot gas conduit ( 6 ) to provide a defrosting mode for the evaporator ( 4 ).

The invention relates to a refrigerating circuit and to a method ofselectively cooling or defrosting an evaporator of a refrigeratingcircuit.

Refrigerating system evaporators having a plurality of refrigerant pipesare well-known in the art. Refrigerant is flown through these pipes foreffecting a heat exchange with an ambient air flow. Refrigerant flowdirection and air flow direction often constitute a counter-flowrelationship. It is also known to use the same pipes in a defrostingoperation by flowing a hot gas therethrough. During a defrostingoperation, however, the problem arises that one side of the evaporator(hot gas outlet) is not fully defrosted and the ice build up at thisside remains unmelted. Moreover, at the other side of the evaporator(hot gas inlet) some of the water generated in the defrosting procedurenormally evaporates, which leads to heavy ice build-up in parts of therefrigerating system that are still below 0° C. Refrigerating systemsoften comprise a Cu pipe serpentine, which is for example located in thefloor of the refrigerating system, to which the evaporator is mounted,and helps in the defrosting operation by carrying hot fluid.

Accordingly, it would be beneficial to provide a refrigerating circuithaving an evaporator, whose defrosting can be carried out in anenergy-efficient manner.

Exemplary embodiments of the invention include a refrigerating circuitcomprising a compressor, a condenser/gas cooler, an expansion device, anevaporator, and refrigerant conduits circulating a refrigeranttherethrough. The evaporator comprises refrigerant piping comprising aplurality of substantially horizontal layers, each layer comprising aplurality of pipes, the pipes being substantially perpendicular to anair flow direction from an air inlet region to an air outlet region ofthe evaporator. A pipe selected from the group of the second pipe to thelast but one pipe in the air flow direction in the bottom layer formsthe entry pipe of the evaporator. The entry pipe is connectable with theexpansion device to provide a refrigerating mode, and the entry pipe isconnectable with a hot gas conduit to provide a defrosting mode for theevaporator.

Exemplary embodiments of the invention further include a method ofselectively cooling or defrosting an evaporator of a refrigeratingcircuit, the method comprising the steps of compressing a refrigerant;flowing the refrigerant through a gas cooler/condenser and an expansiondevice, when cooling is selected, or flowing the refrigerant through ahot gas by-pass conduit, when defrosting is selected; flowing therefrigerant through refrigerant piping of the evaporator, therefrigerant piping comprising a plurality of substantially horizontallayers, each layer comprising a plurality of pipes; and flowing airthrough the evaporator with the air flow direction being substantiallyperpendicular to the orientation of the pipes. The refrigerant entersthe refrigerant piping of the evaporator at a pipe of the group from thesecond pipe to the last but one pipe in the bottom layer.

Embodiments of the invention are described in greater detail below withreference to the Figures wherein:

FIG. 1 shows a schematic of an exemplary evaporator and its integrationin a refrigerating circuit in accordance with the present invention.

FIG. 1 shows a portion of a refrigerating circuit in accordance with anembodiment of the present invention in a schematic manner. As thecompressor and the condenser/gas cooler are well-known elements in theart, they have been omitted from FIG. 1 for easy readability.

The evaporator 4 is shown in detail. It comprises two layers (8, 10) ofrefrigerant pipes (8 a-8 h, 10 a-10 h). As such evaporators are oftendisposed in the floor region of a refrigerating sales furniture, forexample an island freezer, layer 8 is hereinafter also referred to asthe bottom layer, whereas layer 10 is hereinafter also referred to asthe top layer. Each layer comprises eight refrigerant pipes, which areshown as circles giving their representation a cross-sectionalappearance, which indicates that the pipes run perpendicular to thedrawing plane. The pipes are numbered with regard to the air flowdirection 12, which is from left to right in the schematic of FIG. 1. 8a is the first pipe with regard to the air flow direction, 8 b thesecond pipe, . . . , and 8 h is the eighth and last pipe with regard tothe air flow direction. An analogous numbering is adhered to for the toplayer 10.

The refrigerant pipes are interconnected by connection elements, whichare schematically depicted by solid lines and dashed lines. The solidlines represent connection elements that are disposed towards the userfrom the drawing plane, whereas the dashed lines represent connectionelements behind the drawing plane. In this manner, the pipes 8 a to 8 hand 10 a to 10 h combine with the connection elements to form arefrigerant serpentine whose long legs run back and forth through thedrawing plane. This piping is used to flow a refrigerant through theevaporator, with the detailed description of the connection setup andthe resulting refrigerant flow given below.

The third pipe with regard to the air flow direction 12 in the bottomlayer 8, i.e. pipe 8 c, hereinafter also referred to as entry pipe, isin connection to an evaporator inlet section 14 of the refrigerantconduits. Said evaporator inlet section is selectively connected to ahot gas conduit 6 or the expansion device 2 of the refrigeratingcircuit. According means (not shown) for enabling a flow connectionbetween the evaporator inlet section 14 and either the expansion device2 or the hot gas conduit 6 and blocking the respective other of theexpansion device 2 and the hot gas conduit 6 are well-known in the artand therefore not described in detail. The connection with the expansiondevice 2 is selected for a refrigerating mode, whereas the connectionwith the hot gas conduit 6 is selected for a defrosting mode.

In the embodiment shown in FIG. 1 the hot gas conduit 6 originatesbetween the compressor and the condenser/gas cooler. Thus, itestablishes a by-pass conduit, diverting the refrigerant after itscompression and before its cooling in the condenser/gas cooler from theconventional refrigerating circuit. It is apparent that the junctionbetween the compressor and the condenser/gas cooler may compriseappropriate means for guiding the refrigerant either into the hot gasconduit 6 or towards the condenser/gas cooler. The hot gas conduit 6 mayalso comprise an expansion device for controlling thetemperature/pressure of the refrigerant upon entering the evaporator 4in the defrosting mode.

As mentioned above, the refrigerant enters the evaporator 4 at the entrypipe 8 c. From there it is flown through a first section 18 of therefrigerant piping of the evaporator 4. The first section comprises thepipes 8 c, 8 d, . . . , 8 g, and 8 h, which are the entry pipe 8 c andall pipes on the bottom layer that are downstream thereof. These pipesare interconnected by first connection elements 20. The refrigerant isflown substantially perpendicular to the air flow direction in the pipesand substantially in a co-flow relationship with the air flow direction12 in the first connection elements 20 towards the end of the evaporator4.

From pipe 8 h the refrigerant is flown through the second section 22 ofthe refrigerant piping of evaporator 4. The second section 22 ofrefrigerant piping comprises the pipes on the top layer from the end ofthe evaporator 4 to the pipe that is on the same level as the entry pipewith regards to the air flow direction 12, in this embodiment the pipe10 c. The pipes of the second section 22 of the refrigerant piping areinterconnected by second connection elements 24. The refrigerant flow inthe pipes 10 c to 10 h of the second section 22 of refrigerant piping issubstantially perpendicular to the air flow direction 12. Therefrigerant flow in the second connection elements 24 exhibits asubstantially counter-flow relationship with the air flow direction 12.

From pipe 10 c the refrigerant is flown through a third section 26 ofthe refrigerant piping of evaporator 4, which is—in refrigerant flowdirection—comprised of the pipes 8 b, 10 b, 10 a, and 8 a. Accordingly,pipe 8 a is the exit pipe of the evaporator. It is connected to theevaporator outlet section 16 of the refrigerant conduits, which leadsthe refrigerant back to the compressor.

The above-described structure of the evaporator 4 according to anexemplary embodiment of the invention has a number of implications forthe defrosting and the refrigerating modes. In the refrigerating mode itis the primary objective to generate a heat transfer between therefrigerant and the air flow that is as efficient as possible. Thecounter-flow relationship between the refrigerant and the air flowdirection 12 in the second section 22 of the refrigerant piping providesfor very good heat transfer conditions. Moreover, the third section 26of the refrigerant piping provides for an extended region, where therefrigerant is at its warmest in the evaporator and the air flow is alsoat its warmest right after entering the evaporator 4. This set-upprovides for a maximum heating of the refrigerant and thus for a maximumheat transfer from the air flow before the refrigerant leaves theevaporator 4 through the exit pipe 8 a. In the case that the refrigeranthas been evaporated in the first or second section (18, 22) of therefrigerant piping, the third section 26 allows for a maximum amount ofsuper-heating of the gaseous refrigerant.

In the defrosting mode the above-described structure of the evaporator 4is particularly efficient for a number of reasons. In the exemplaryembodiment of FIG. 1, the hot refrigerant, after by-passing thecondenser/gas cooler and the expansion device 2, enters the evaporator 4at entry pipe 8 c. At the point of entry the refrigerant is the warmestand has the biggest effect in melting the ice build-up in the evaporator4. Thus, the region around the entry pipe 8 c and the downstream portionthereof in the bottom layer receive the most heat, especially in thebeginning stages of the defrosting operation. An advantageous effectthereof is that the support structure to which the evaporator 4 isattached, for example the floor portion of an island freezer, is warmedup starting in the middle region and expanding to the sides. A warmingof the support structure at an early stage of the defrosting operationprevents a scenario wherein ice is melted somewhere in the evaporator 4and the water is re-frozen at the support structure, when supposed todrain out of the evaporator 4. The set-up provides for the supportstructure, which may be slightly inclined, to be an ideal gutter forwater generated by melting the ice in all parts of the evaporator 4 atlater stages of the defrosting operation. Another advantage is thatwater vapour which may be generated around the entry pipe 8 c, wherecontinuous heating is effected by flowing hot fluid through therefrigerant piping, cannot easily leave the evaporator 4 and re-freezein other parts of the refrigerating system, where the temperature isstill below 0° C. In other words, instead of generating ice build-upoutside of the evaporator 4, the water vapour helps in defrosting theevaporator 4 from the middle region towards the sides.

The foregoing discussion shows that the evaporator 4 of the exemplaryembodiment of the invention in FIG. 1 has a structure that allows forextremely energy-efficient defrosting of the evaporator 4. This evenallows basing the defrosting of the evaporator solely on the by-passconduit, when CO₂ is used as a refrigerant. The refrigerant piping ofthe evaporator 4 of the exemplary embodiment is not designed in a way tosustain CO₂ in a liquid phase. That means that, when CO₂ is used asrefrigerant, the condensation energy is not at the disposal of thedefrosting process, which is compensated for by the energy-efficientlayout of the evaporator 4.

As mentioned before, the hot gas conduit 6 may be a by-pass conduit tothe refrigerating circuit. It may also be part of an independentdefrosting circuit. It is apparent that in addition to the flowswitching means between the expansion device 2 and the hot gas conduit6, second guiding means would be necessary to direct the fluid comingout of the evaporator 4 into the defrosting circuit or the refrigerantcircuit. The defrosting circuit would in that case need additional meansfor generating fluid circulation, for example a compressor.

The hot gas conduit 6 may carry a fluid in a liquid or gaseous state tothe evaporator, depending on the specific embodiment of the invention.

Instead of comprising two layers the evaporator 4 may comprise three ormore layers as well. This would lead to some changes as to how the pipesare connected with connection elements. Assume an evaporator having thetwo layers 8 and 10, as depicted, as well as an additional third layer.Assume that the eight pipes of the third layer are denoted 30 a, 30 b, .. . , 30 g, and 30 h, in analogy with the first layer 8 and the secondlayer 10. The first section 18 of the refrigerant piping would have thesame structure as in the exemplary embodiment of FIG. 1. However, thesecond section 22 of the refrigerant piping would have a fairlydifferent layout. It would comprise the pipes 10 c to 10 h of theintermediate layer and the pipes 30 c to 30 h of the third layer. Aplurality of options can be thought of as to how to connect these pipeswith each other. A first option would be connecting—in refrigerant flowdirection—pipes 10 a, 30 h, 10 b, 30 g, 10 f, etc., forming a kind ofsawtooth wave shape of the connection elements.

Another option would be connecting—in refrigerant flow direction—pipes10 h, 30 h, 30 g, 10 g, 10 f, 30 f, etc., forming a kind of square waveshape of the connection elements. Both options have in common that therefrigerant flows in a generally counter-flow relationship with respectto the air flow direction 12 in the second section 22 of the refrigerantpiping. Additional options, for example options combining the twoabove-described ways of connecting the individual pipes, can be thoughtof. It is apparent that the connection options increase with the numberof layers of refrigerant pipes. As far as the third section 26 of therefrigerant piping is concerned, a lot of options for connectionsstarting at the last pipe of the second section 22, i.e. either 10 c or30 c, to the exit pipe 8 a exist. As is clear from simple geometricconsiderations, there is no possibility of connecting all pipes withoutany connection elements exhibiting co-flow relationship with the airflow direction 12. Therefore, a lot of secondary considerations are leftto be considered by the designer when establishing the connectionelement layout.

Exemplary embodiments of the invention, as described above, allow forenergy-efficient cooling of the air flow through an evaporator in arefrigerating mode as well as for energy-efficient defrosting of saidevaporator in a defrosting mode. Introducing the hot gas into a pipe inthe middle portion of the bottom layer of the evaporator in thedefrosting mode provides for a number of advantages. The region aroundthe point of entry of the hot gas will be heated most and will bedefrosted quickest. Therefore, the support structure, to which theevaporator is mounted, will be defrosted in the beginning stages of adefrosting operation and thus will provide for an ice-free surface,which is ideal for receiving and draining the water that is generatedthroughout the defrosting process. Moreover, the water vapour, which isgenerated in the most heated portion of the evaporator during thedefrosting process, will not be able to leave the evaporator, as it willnot stay a vapour on its way to the end portions of the evaporator.Thus, energy losses due to the heated vapour leaving the evaporator tobe defrosted are minimized and ice built-up in other parts of therefrigerating system, caused by said water vapour, is prevented. Theseaspects allow for a highly efficient defrosting of the evaporator,eliminating the need for or at least reducing the extent of additionalmeans for defrosting in the support structure or in the evaporatoritself. This even holds true, when CO₂ is used as the hot gas in thedefrosting operation, which is fundamentally less attractive for use indefrosting, as no condensation takes place at pressures common to theseevaporators. The defrosting operation in a refrigerant circuit inaccordance with an embodiment of the invention is so energy-efficientthat shorter defrosting times can be achieved than with electricdefrosting. This time duration advantage is paired with the overallsimplification of not having an additional electric defrosting systemintegrated into a refrigerating system.

In a further embodiment of the invention, the hot gas conduit is aby-pass conduit originating between the compressor and the expansiondevice and ending between the expansion device and the evaporator. Thisstructure allows for using the same fluid for the refrigeratingoperation as well as for the defrosting operation, which is verycost-efficient. It also eliminates the need for having a full secondfluid circuit for the fluid of the defrosting operation and eliminatesthe need for ensuring a strict separation of the refrigerating fluid andthe defrosting fluid. This layout also allows for a minimum amount ofpiping used and thus for a very compact design of the refrigeratingcircuit.

Furthermore, the refrigerant entry pipe may be a pipe in the first halfof the evaporator in the air flow direction. It is also possible that afirst section of the refrigerant piping of the evaporator comprises theentry pipe and the pipes on the bottom layer that are downstream of theentry pipe with regard to the air flow direction. This allows for anearly and thorough heating of the bottom region of the evaporator in thedefrosting process, which is beneficial to the draining of the meltedwater during the later stages of the defrosting. This first sectionleaves the beginning of the evaporator in the air flow direction out,which leaves the option of flowing the refrigerant therethrough shortlybefore leaving the evaporator, which in turn is beneficial in therefrigerating mode. Therefore, this layout is a good basis for achievingan excellent trade-off between the refrigerating and the defrostingmodes.

It is furthermore possible that first connection elements connectrespective adjacent pipes of the first section of the refrigerant pipingof the evaporator, such that in operation the refrigerant flows in aco-flow relationship with the air flow direction in the first connectionelements. This allows for an advantageous heating of the bottom layer,and therefore of the underlying support structure, from a middle regiontowards an end region of the evaporator.

In another embodiment of the invention, a second section of therefrigerant piping of the evaporator comprises the pipes on the level ofand downstream from the entry pipe with regard to the air flow directionabove the bottom layer. It is also possible that second connectionelements connect the pipes of the second section of the refrigerantpiping of the evaporator, such that in operation the refrigerant flowsin an overall counter-flow relationship with the air flow direction inthe second connection elements. This allows for using an advantageouscounter-flow relationship between the refrigerant and the air flow inthe refrigerating mode. This layout furthermore allows for implementingthe beneficial counter-flow for one or a plurality of layers above thebottom layer, i. e. in the second section of the refrigerant piping.

Moreover, it is possible that the first pipe in the air flow directionin the bottom layer is an exit pipe. This exit pipe may be connected toan evaporator outlet section of the refrigerant conduits. Having therefrigerant leave the evaporator in the first pipe in the air flowdirection in the bottom layer ensures that the refrigerant flows lastthrough the inlet region of the evaporator with regard to the air flow.In the refrigerating mode, this leads to a region of heat exchangebetween the air flow and the refrigerant, when they are both in theirwarmest state throughout the evaporator. This allows for the maximumamount of superheating of the refrigerant, when in gaseous form already,which provides for maximum use of the energetic capacity of therefrigerant in the refrigerating process.

In a further embodiment, a third section of the refrigerant piping ofthe evaporator comprises the pipes upstream of the refrigerant entrypipe with regard to the air flow direction. This allows for an extendedregion of heat transfer between the air flow and the refrigerant, wherethey are both at their substantially warmest in the refrigerating mode.It allows for that region to include all layers, forming a heat exchangeregion with above described properties across the hole cross-section ofthe air flow.

The refrigerant piping of the evaporator may comprise two or threelayers. An evaporator having four, five or more layers can also bethought of. Each layer of the refrigerant piping of the evaporator maycomprise five to ten pipes, particularly six to eight pipes. Thesenumbers of pipes have been found to be beneficial for an efficient heatexchange both in the refrigerating and the defrosting mode. Depending onthe application, less than five pipes or more than ten pipes may alsoconstitute a good layer size.

In a further embodiment, the refrigerant entry pipe is the second orthird pipe in the air flow direction in the bottom layer of therefrigerant piping of the evaporator. This allows for the hot gasentering the evaporator towards the middle in the refrigerating mode,advantageously heating the middle portion of the bottom region of theevaporator first in a defrosting mode. It also leaves room for having aheat exchange area of relatively warm refrigerant and relatively warmair flow in the beginning of the evaporator with regard to the air flowdirection, when the system is operated in the refrigerating mode.

The refrigerant may be CO₂. It can also be R22 or R404A or any otherrefrigerant suitable to the refrigerating circuit.

In an exemplary embodiment, the air flow in the evaporator is in therefrigerating mode cooled down to a temperature below 0° C. In otherwords, the invention is suitable for freezers and below 0° C.refrigerating systems, where defrosting is a big issue.

It is also possible that the refrigerating circuit comprises twoexpansion devices and two evaporators, a first expansion device and afirst evaporator forming a below 0° C. refrigerating portion of therefrigerating circuit, the second expansion device and the secondevaporator forming an above 0° C. refrigerating portion of therefrigerating circuit. Accordingly, the invention can be applied to adual system including a freezer and a refrigerator. In this case, thedefrosting may be carried out on the freezing portion or on therefrigerating portion or on both portions. It is apparent that accordingpiping and according compressing means will be necessary.

With the method of selectively cooling or defrosting an evaporator of arefrigerating circuit according to exemplary embodiments of theinvention, as described above, the same advantages can be attained aswith the refrigerating circuit. This method can be developed further bymethod steps corresponding to the features as described with regard tothe refrigerating circuit. In order to avoid redundancy such embodimentsand developments of the method of selectively cooling or defrosting anevaporator of a refrigerating circuit are not repeated.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

REFERENCE NUMERALS

-   2 Expansion device-   4 Evaporator-   6 Hot gas conduit-   8 Bottom layer of refrigerant piping of evaporator-   10 Top layer of refrigerant piping of evaporator-   12 Air flow direction-   14 Evaporator inlet section of refrigerant conduits-   16 Evaporator outlet section of refrigerant conduits-   18 First section of refrigerant piping of evaporator-   20 First connection elements-   22 Second section of refrigerant piping of evaporator-   24 Second connection elements-   26 Third section of refrigerant piping of evaporator

1-16. (canceled)
 17. Refrigerating circuit comprising a compressor, acondenser/gas cooler, an expansion device, an evaporator, andrefrigerant conduits circulating a refrigerant therethrough, wherein theevaporator comprises refrigerant piping comprising a plurality ofsubstantially horizontal layers each layer comprising a plurality ofpipes the pipes being substantially perpendicular to an air flowdirection from an air inlet region to an air outlet region of theevaporator, wherein a pipe selected from the group of the second pipe tothe last but one pipe in the bottom layer forms the entry pipe of theevaporator, wherein the entry pipe is connectable with the expansiondevice to provide a refrigerating mode, wherein the entry pipe isconnectable with a hot gas conduit to provide a defrosting mode for theevaporator, and wherein a first section of the refrigerant piping of theevaporator comprises the entry pipe and the pipes on the bottom layerthat are downstream of the entry pipe with regard to the air flowdirection.
 18. Refrigerating circuit according to claim 17, wherein thehot gas conduit is a by-pass conduit originating between the compressorand the expansion device and ending between the expansion device and theevaporator.
 19. Refrigerating circuit according to claim 17, wherein therefrigerant entry pipe is a pipe in the first half of the evaporator inthe air flow direction.
 20. Refrigerating circuit according to claim 17,wherein first connection elements connect respective adjacent pipes ofthe first section of the refrigerant piping of the evaporator, such thatin operation the refrigerant flows in a co-flow relationship with theair flow direction in the first connection elements.
 21. Refrigeratingcircuit according to claim 17, wherein a second section of therefrigerant piping of the evaporator comprises the pipes on the level ofand downstream from the entry pipe with regard to the air flow directionabove the bottom layer.
 22. Refrigerating circuit according to claim 21,wherein second connection elements connect the pipes of the secondsection of the refrigerant piping of the evaporator, such that inoperation the refrigerant flows in an overall counter-flow relationshipwith the air flow direction in the second connection elements. 23.Refrigerating circuit according to claim 17, wherein the first pipe inthe air flow direction in the bottom layer is an exit pipe. 24.Refrigerating circuit according to claim 21, wherein a third section ofthe refrigerant piping of the evaporator comprises the pipes upstream ofthe refrigerant entry pipe with regard to the air flow direction. 25.Refrigerating circuit according to claim 17, wherein the refrigerantpiping of the evaporator comprises 2 or 3 layers.
 26. Refrigeratingcircuit according to claim 17, wherein each layer of the refrigerantpiping of the evaporator comprises 5 to 10 pipes, particularly 6 to 8pipes.
 27. Refrigerating circuit according to claim 17, wherein therefrigerant entry pipe is the second or third pipe in the air flowdirection in the bottom layer of the refrigerant piping of theevaporator.
 28. Refrigerating circuit according to claim 17, wherein therefrigerant is
 29. Refrigerating circuit according to claim 17, whereinthe air flow in the evaporator is in the refrigerating mode cooled downto a temperature below 0° C.
 30. Refrigerating circuit according toclaim 17, wherein the refrigerating circuit comprises two expansiondevices and two evaporators, a first expansion device and a firstevaporator forming a below 0° C. refrigerating portion of therefrigerating circuit, the second expansion device and the secondevaporator forming an above 0° C. refrigerating portion of therefrigerating circuit.
 31. Method of selectively cooling or defrostingan evaporator of a refrigerating circuit, the method comprising:compressing a refrigerant, flowing the refrigerant through a gascooler/condenser and an expansion device, when cooling is selected, orflowing the refrigerant through a hot gas by-pass conduit, whendefrosting is selected, flowing the refrigerant through refrigerantpiping of the evaporator, the refrigerant piping comprising a pluralityof substantially horizontal layers each layer comprising a plurality ofpipes, and flowing air through the evaporator with the air flowdirection being substantially perpendicular to the orientation of thepipes, wherein the refrigerant enters the refrigerant piping of theevaporator at a pipe of the group from the second pipe to the last butone pipe in the bottom layer, and wherein the refrigerant flows througha first section of the refrigerant piping of the evaporator comprisingthe entry pipe and the pipes on the bottom layer that are downstream ofthe entry pipe with regard to the air flow direction.